National safety surveillance of quadrivalent recombinant influenza vaccine in Taiwan during NH 20/21

BACKGROUND: During the COVID-19 pandemic, the need for influenza vaccine significantly increased in the initial weeks of the 2020–2021 influenza vaccination campaign season in Taiwan. To meet this demand, the Taiwanese government therefore purchased additional influenza vaccines via special import, including 350,000 doses of quadrivalent recombinant influenza vaccines (RIV4, Flublok Quadrivalent). Approved in the United States since 2016, there were limited numbers of published studies regarding RIV4 outside America. We utilized the national passive surveillance system consisting adverse event (AE) reports following RIV4 immunization to describe its safety profiles in Taiwan. METHODS: We obtained the database from the Taiwan National Adverse Drugs Reactions Reporting System and collected reports from January 2021 to July 2021, which was at least one month after RIV4 immunization. AE reporting rates were calculated based on the total administered doses. RESULTS: Eight AEs were reported among 200,287 administered doses, which led to a reporting rate of 3.99 AEs per 100,000 doses administered. The mean age of the reported individuals were 47.53 years, and women (75%) were the predominant gender. Most adverse events started within the first day after immunization, with one reported as starting 4 days after vaccination. Among the 8 cases, 75% (n = 6) were non-serious and the most common symptoms were erythematous skin rashes with pruritus. Two cases were listed as serious based on the criteria of “other clinically significant medical conditions”, but neither was judged to have a causal relationship with RIV4 immunization. CONCLUSION: The Taiwan national passive surveillance data supported the safety profiles of RIV4 in Taiwan population.